In-depth comparison of the metabolic and pharmacokinetic behaviour of the structurally related synthetic cannabinoids AMB-FUBINACA and AMB-CHMICA in rats

Abstract

Synthetic cannabinoids receptor agonists (SCRAs) are often almost completely metabolised, and hence their pharmacokinetics should be carefully evaluated for determining the most adequate biomarker in toxicological analysis. Two structurally related SCRAs, AMB-FUBINACA and AMB-CHMICA, were selected to evaluate their in vivo metabolism and pharmacokinetics using male Sprague-Dawley rats. Brain, liver, kidney, blood (serum) and urine samples were collected at different times to assess the differences in metabolism, metabolic reactions, tissue distribution and excretion. Both compounds experimented O-demethyl reaction, which occurred more rapidly for AMB-FUBINACA. The parent compounds and O-demethyl metabolites were highly bioaccumulated in liver, and were still detected in this tissue 48 h after injection. The different indazole/indole N-functionalisation produced diverse metabolic reactions in this moiety and thus, different urinary metabolites were formed. Out of the two compounds, AMB-FUBINACA seemed to easily cross the blood-brain barrier, presenting higher brain/serum concentrations ratio than AMB-CHMICA.

Fig. 1. Elucidation of hydroxylated AMB-CHMICA metabolites by UHPLC-HRMS.

Low energy and high energy spectra for parent compound, metabolite M2, and metabolite M4 are shown. Red text and dashed lines refer to AMB-CHMICA, green to metabolite M2, and purple to metabolite M4. Mass errors have been calculated in parts per million (ppm), as follows: $\mathrm{ppm}=\frac{\mathrm{accurate}\mathrm{mass}-\mathrm{exact}\mathrm{mass}}{\mathrm{exact}\mathrm{mass}}\cdot {10}^6$.

Fig. 2. Proposed metabolic pathway for AMB-FUBINACA.

Red moieties in compound structures indicate biotransformations. Tissue names indicate the prevalence of the metabolite.

Fig. 3. Proposed metabolic pathway for AMB-CHMICA.

Red moieties in compound structures indicate biotransformations. Tissue names indicate prevalence of the metabolite.

Fig. 4. SCRAs and metabolites distribution over time.

Distribution of the parent compound and metabolites of a AMB-FUBINACA and b AMB-CHMICA in the different matrices analysed over time. Stick height represents analytical response of the compound.

Fig. 5. Proposed fragmentation for the two SCRAs.

Proposed chemical structure for the accurate-mass fragments observed for a AMB-FUBINACA and b AMB-CHMICA. Below the proposed structure of each fragment ion it is displayed its corresponding m/z.